T-amp potentiometer problems.

[Jim McPherson]

At the recommendation of many, I swaped out the pot/switch on my T-Amp. I used the 100K alps from radio shack. While it works, the amp now reaches full volume in about 1/8th of a turn with line out from an iPod. This likely stems from the fact that the original pot was 50k and the new one is 100k. It seems like adding a parallel resistor "somewhere" would solve my problem, but I can't figure out where to put it. Any ideas?

-Jim

 

[Panelhead]

At the recommendation of many, I swaped out the pot/switch on my T-Amp. I used the 100K alps from radio shack. While it works, the amp now reaches full volume in about 1/8th of a turn with line out from an iPod. This likely stems from the fact that the original pot was 50k and the new one is 100k. It seems like adding a parallel resistor "somewhere" would solve my problem, but I can't figure out where to put it. Any ideas?

-Jim

This is a taper issue, not impedance. Are you sure the Alps is a log taper and not a linear?
Some pots exhibit differing tapers even if they are log. The Alpha's I used before ramped up very quickly. The PEC's used now are much more gradual.
Using each with the same impdeance, the matched volume was 9 o'clock on the Alpha and 10:30 - 11:00 on the PEC.


George

 

[kiang]

go for a 50K ALPS LOG potentiometer.

 

[Leolabs]

I would go for 100k linear with a 15k bypass to ground

 

[zanash]

you will get more usable range with a log pot......

Hve you checked your wiring ?

 

[Jim McPherson]

Thanks for the suggestions all!

Zanash:
Funny you should say that. Just for fun last night I cut all the wires going to the pot and re-wired very carefully and now it works perfectly. Well, almost perfect, at the low end of the range the speakers are not well balanced... but that's what I get for using a $3.29 pot.

Thanks for your help!

-Jim

 

[motherone]

I suggest getting one of the 50k Alps Blue Velvet's from Tangent's audio shop (www.tangentsoft.net)... They're only $15, have great channel matching, and will make you glad you tossed out the rat-shack alps.

 

[zanash]

glad to be of help.........


I had similar problems with a new vol pot on a nad 3020.....intrestingly the volume pot dictated the sound of that amp. The classic warm presentation is totally down to the vol pot.

 

[sx881663]

Pot question

Jim,
Now is a good time to jumper out the on board coupling caps and put quality film units from the pot to the input pin. If you do this you have to remove the resistors to ground, R01 and R02 on the new SI board. This will give you a bigger improvement than the new pot.
Roger

 

[motherone]

Re: Pot question

Jim,
Now is a good time to jumper out the on board coupling caps and put quality film units from the pot to the input pin. If you do this you have to remove the resistors to ground, R01 and R02 on the new SI board. This will give you a bigger improvement than the new pot.
Roger

Hm.. I would actually disagree. I actually wound up doing this because I messed up a few pads on the board. I highly recommend only changing the feedback resistor and the capacitors, as it's too easy to mess the board up otherwise, and the changes aren't appreciable. To me, the biggest improvements on the SI were from the following:

1) Increasing size and quality of onboard PSU supply cap
2) Replacing potentiometer with better quality device. Honestly, this can be a panasonic EVJ or ALPS or whatever -- the stock one just flat out sucks!
3) Increasing the size and quality of the onboard input coupling cap
4) Changing the feedback resistors from 36k to achieve unity-gain.

I think the only other mods that may make a marked imrpovement are the replacement of the inductors as others have stated on here. I still haven't had a chance to try this yet, but hope to soon.

 

[sx881663]

Re: Re: Pot question

Hm.. I would actually disagree. I actually wound up doing this because I messed up a few pads on the board. I highly recommend only changing the feedback resistor and the capacitors, as it's too easy to mess the board up otherwise, and the changes aren't appreciable. To me, the biggest improvements on the SI were from the following:

1) Increasing size and quality of onboard PSU supply cap
2) Replacing potentiometer with better quality device. Honestly, this can be a panasonic EVJ or ALPS or whatever -- the stock one just flat out sucks!
3) Increasing the size and quality of the onboard input coupling cap
4) Changing the feedback resistors from 36k to achieve unity-gain.

I think the only other mods that may make a marked imrpovement are the replacement of the inductors as others have stated on here. I still haven't had a chance to try this yet, but hope to soon.

I will agree to disagree. I have done incremental changes to 3 units now, testing each change before proceeding. 2 were put in new cases with SMPS power. Replacing the stacked film input cap with a quality polypropylene type is a huge improvement sonically. You don’t need to risk the circuit board at all. Just jumper out the original caps, remove r01 and r02 and then put the new caps off board connected from the volume control wipers to the input pins on the board. You really need to try this to find out how much difference it makes. Replacing the pot is a good upgrade, don’t get me wrong I just think that the caps are a lot more improvement for the work and expense.
Roger

 

[motherone]

Re: Re: Re: Pot question

I will agree to disagree. I have done incremental changes to 3 units now, testing each change before proceeding. 2 were put in new cases with SMPS power. Replacing the stacked film input cap with a quality polypropylene type is a huge improvement sonically. You don’t need to risk the circuit board at all. Just jumper out the original caps, remove r01 and r02 and then put the new caps off board connected from the volume control wipers to the input pins on the board. You really need to try this to find out how much difference it makes. Replacing the pot is a good upgrade, don’t get me wrong I just think that the caps are a lot more improvement for the work and expense.
Roger

I'm not disagreeing on the caps -- I just think that the stock pot has terrible tracking, which is why I think it should be tossed. Panasonic EVJs are pretty cheap ($2-3 on digikey if I remember right), so there's no reason not to put a quality one in, either.

I've done the replacement with Polypropylene, but I'm going to try going with a 4.7uf BG-N on my next mod, just to see if I can keep the size small and if there's a massive difference in sound quality. if not, I'll recommend that route, since you don't have to worry about placing stuff off-board, other than the pot itself.

 

[sx881663]

Re: Re: Re: Re: Pot question

I'm not disagreeing on the caps -- I just think that the stock pot has terrible tracking, which is why I think it should be tossed. Panasonic EVJs are pretty cheap ($2-3 on digikey if I remember right), so there's no reason not to put a quality one in, either.

I've done the replacement with Polypropylene, but I'm going to try going with a 4.7uf BG-N on my next mod, just to see if I can keep the size small and if there's a massive difference in sound quality. if not, I'll recommend that route, since you don't have to worry about placing stuff off-board, other than the pot itself.

Guess I have been lucky as the pots I have had are ok, not great but usable. Knowing the difference it made in my preamp going from a black beauty to a DACT stepped attenuator leaves no doubt in my mind this is a good place for improvement. Would like to use a DACT but just too expensive for this job. Think I have a Nobel 10k around I could try. Will let you know what I think.
I certainly will agree that an on board cap solution would be best but quality in that small of form factor is very questionable. BG might be the best on board solution but if you have the room why not off board? I mounted them on the outside of the battery compartment of a unit I did for a friend. Added twisted lead wires to prevent excessive noise pickup. Unit sounded very nice when done and that really is the bottom line.
Roger

 

[motherone]

Re: Re: Re: Re: Re: Pot question

Guess I have been lucky as the pots I have had are ok, not great but usable. Knowing the difference it made in my preamp going from a black beauty to a DACT stepped attenuator leaves no doubt in my mind this is a good place for improvement. Would like to use a DACT but just too expensive for this job. Think I have a Nobel 10k around I could try. Will let you know what I think.

I'm using the 10k nobles (black metal bodied ones) in mine. They work great! Picked a whole slew of NOS ones on ebay at $5/each.

I certainly will agree that an on board cap solution would be best but quality in that small of form factor is very questionable. BG might be the best on board solution but if you have the room why not off board?

Well, I'm trying to see what I can get out of this thing keeping most of the parts on-board. I do have externally mounted caps right now, and I just want to see if there's a big difference. If there isn't, why go to the trouble?

I mounted them on the outside of the battery compartment of a unit I did for a friend. Added twisted lead wires to prevent excessive noise pickup. Unit sounded very nice when done and that really is the bottom line.
Roger

I agree. Ultimately, it's whatever works best for you. Like I said, I have two rather large 160v 2.2uF PP caps in my "reference" one. My only intention is to list the mods that I think are the most worthwhile. Afterall, if you're going to take it apart and upgrade the critical stuff, why not do it all in one shot?

 

[sx881663]

Question on posting

motherone,
Points well taken! My only reservation is how much effort is the unit worth? At some point it makes sense to switch to a UcD or something from 41Hz. The first reference unit is obviously a different case where you want to find out what they will do. I have reached that point and my unit is now as far as I want to go except for the Nobel pot I mentioned. I am putting my efforts into the excellent UcD400 modules.
My posting question, how do you split up the quotes as you did on your last one? I can't seem to do this.
Roger

 

[motherone]

Re: Question on posting

motherone,
Points well taken! My only reservation is how much effort is the unit worth? At some point it makes sense to switch to a UcD or something from 41Hz. The first reference unit is obviously a different case where you want to find out what they will do. I have reached that point and my unit is now as far as I want to go except for the Nobel pot I mentioned. I am putting my efforts into the excellent UcD400 modules.

I'm with you there. I have too many freakin' amps I want to build, including the UCD's. The nice thing about the SI's, though, is that I have a ton of the parts needed to upgrade them just laying around, so they're a very cheap project!

My posting question, how do you split up the quotes as you did on your last one? I can't seem to do this.
Roger

If you look in the text, they have code encased in []'s .. I just copy and past the quote sections. You close out the paragraph with the [] and a slash in front of the argument.

The other option is that you can use the "quote" button to do most of it for you.

 

[sx881663]

Re: Re: Question on posting

I'm with you there. I have too many freakin' amps I want to build, including the UCD's. The nice thing about the SI's, though, is that I have a ton of the parts needed to upgrade them just laying around, so they're a very cheap project!

Yes, but not cheap results.

If you look in the text, they have code encased in []'s .. I just copy and past the quote sections. You close out the paragraph with the [] and a slash in front of the argument.

The other option is that you can use the "quote" button to do most of it for you. [/B]

Had to try it out, thanks.
Roger

 

[windzilla]

Bi-wire, "passive" Bi-amp Pot question

I am somewhat new to DIY audio, I have a little working knowledge of electronics, but want to make sure about this before i go and ruin my t-amps.

I wanted to know if two t amps could be used in parallel (one for lows, one for highs) on bi-wire capable speakers, and if I could get rid of the stock Pots, and use one stereo pot to control both volumes. I have heard these amps are not bridgeable but I am not really bridging with this (I think). Any input is greatly appreciated.

In addition, would it be advantageous to use a non-metallic project box vs. steel or Al? Do the electronic insulating properties of plastic have any advantages over metal that would outweigh the limited need for heat dispersion in these little people?

Thanks

W

 

[sx881663]

Re: Bi-wire, "passive" Bi-amp Pot question

I am somewhat new to DIY audio, I have a little working knowledge of electronics, but want to make sure about this before i go and ruin my t-amps.

I wanted to know if two t amps could be used in parallel (one for lows, one for highs) on bi-wire capable speakers, and if I could get rid of the stock Pots, and use one stereo pot to control both volumes. I have heard these amps are not bridgeable but I am not really bridging with this (I think). Any input is greatly appreciated.

In addition, would it be advantageous to use a non-metallic project box vs. steel or Al? Do the electronic insulating properties of plastic have any advantages over metal that would outweigh the limited need for heat dispersion in these little people?

Thanks

W

I would guess you would be using all of them as full range units? If you are using stock units I would recommend constructing or modifying a pair of cables to have the correct mini plug on one end and an RCA on the other. Tie both inputs together at the mini plug so one signal (R or L) is driving both channels of the amp. Connect each channel to the speaker high or low for biamp. This will give you quite a bit more power to work with and should be worth doing. It won’t be twice the power as the bass hogs it all anyway.
To use one volume control correctly, you will have to build all the channels into one box. This will allow you use one larger power supply for both modules but means you need to mount 8 speaker connectors and have longer speaker cables. If you go this way you might as well mount a few RCA inputs and a selector switch to make it into a neat little integrated amp.
I have been using die cast aluminum cases and they work well. I think they were the Hammond 1590C from Digikey or Mouser. This model would not be big enough for 2 modules and power supply together but they do have larger ones. These provide shielding and heat transfer, both desirable. If you use plastic you will have to drill a lot of holes for ventilation or the unit will shut down with over temperature and might even be a fire hazard.
Good luck, have fun!
Roger